Statement of the Technical Field
The inventive arrangements relate to Microelectromechanical System (“MEMS”) and methods for forming the same, and more specifically to transducers with Integrated Circuits (“ICs”).
Description of the Related Art
MEMS is a technology of very small devices typically between 2 micrometers to 2 millimeters in size. The MEMS devices can include one or more components between 1 to 100 micrometers in size. Conventional MEMS devices are fabricated using molding techniques, plating techniques, wet etching techniques, dry etching techniques, and/or Electro Discharge Machining (“EDM”) techniques. Various materials can be used to create the MEMS devices. Such materials include silicon, polymers, metals and ceramics.
Radio Frequency filters typically occupy a relatively large amount of real estate in an RF system (i.e., >25%). As such, it has been desirable to miniaturize RF filters via MEMS technology, as well as integrate the electronics with the MEMS RF filters as performance can be achieved. In general, there are three techniques for integrating MEMS RF filters with ICs. The three techniques include a pre-processing technique, a post-process technique, and a merged processing technique. The pre-processing technique involves: first fabricating a MEMS device (e.g., MEMS RF filter) on a substrate; isolating the MEMS device using a dielectric layer; and thereafter fabricating the IC. The post-processing technique involves: fabricating the IC on the substrate; isolating the IC using a dielectric layer; and thereafter fabricating the MEMS device. The merged processing technique involves simultaneously fabricating the MEMS device and filter circuitry on a substrate in an interleaving fashion. Typically, the MEMS device is fabricated using a polysilicon material. The ICs are fabricated using thin-film dielectrics and metals (e.g., gold, nickel, aluminum, copper, chromium, titanium, tungsten, platinum and/or silver).
Despite the advantages of integrating RF filters with ICs, the conventional processes for achieving such integration suffer from certain drawbacks. For example, the disposition process of a MEMS device comprising the polysilicon material requires high temperatures (e.g., excess of 1000° C.). The materials that are used to build the ICs have melting points that are much lower (e.g., 300-400° C.) than the temperatures required to fabricate the MEMS devices. Consequently, the ICs may possibly be damaged during the post-processing technique or the merged processing technique as a result. Also, commercially available conventional integrated RF filters exhibit at best an insertion loss of 9 dB, which is considered those skilled in the art as undesirably high. The high insertion loss is primarily due to the use of dielectric films (e.g., Silicon Germanium (“SiGe”)) that are inherently lossy at higher frequencies as a result of doping.